We propose to continue our work in four areas related to the role of growth factors, particularly epidermal growth factor (EGF), in the regulation of cell multiplication: the physical properties of growth factor-cell interaction, the biological response of normal and transformed cells, the specific changes in these physical and biological properties in neoplasia and aging, and the genetic control of growth factor membrane receptors. Availability of complex defined medium will allow us to examine the potency of specific putative growth factors and to evaluate potential synergism of specific combinations of these factors in stimulating cell growth. Human diploid fibroblasts will be passaged in defined medium with various combinations of growth factors and the life span compared to parallel cultures grown with serum supplement. EGF binding studies on aging cells will attempt to characterize the turnover of EGF receptors as a function of normal and precocious aging. Iodination and fractionation of membrane associated proteins, glycoproteins and lipoproteins will set the stage for the development of techniques to isolate and compare EGF receptors from early and late passage human strains. Identical techniques will be used to characterize membrane components of normal rat kidney cells and transformed derivatives which have lost their responsiveness to EGF mitogenic effect and show little or no EGF binding. In this system, transformed cells produce factor(s) which enhance EGF binding to normal cells and stimulate initiation of DNA synthesis. Isolation and characterization of these cell products may be possible through the use of serum-free complex defined medium. Genetic regulation of EGF receptors will be studied by hybridizing cells with and without receptors to determine dominance or recessiveness of receptor expression; these studies may provide clues to the linkage of EGF receptor structural genes to specific chromosomes. Characterization of surface membrane proteins and growth factor receptors during aging and transformation may provide new knowledge of the events limiting cell division and lead us closer to methods of preventing and/or controlling malignant growth.